A steel wire of uniform cross- section of $2\;mm^2$ is heated upto $50^{\circ}$ and clamped rigidly at two ends. If the temperature of wire falls to $30^{\circ}$ then change in tension in wire will be , if coefficient of linear expansion of steel is $1.1 \times 10^{-5}/ ^{\circ} C$ and $Y=2 \times 10^{11} N/m^2$